1. Field of the Invention
This invention relates to a gas refrigerator, especially to a pulse tube refrigerator.
2. Description of the Related Art
In order to produce cold temperature in a pulse tube by gas expansion, it is necessary to cause time-phase displacement in the pressure of vibrating gas and the change of gas volume. Therefore, an orifice type pulse tube refrigerator, as is known in the art, includes mainly a high pressure gas inlet valve, a low pressure gas outlet valve, a regenerator, a cooler, a refrigeration power heat exchanger, a gas smoother, an orifice, which forms phase displacement, and a reservoir system. Such an orifice and a reservoir system are connected to a hot end of a pulse tube thereof. The expansion work is released as heat to the outside by the throttling process of the orifice, which provides the pulse tube with a refrigeration effect. If such a irreversible loss is not produced at the hot end of the pulse tube, the pulse tube does not generate the refrigeration effect. However, the gross refrigeration power per unit mass flow in the pulse tube is very low, which causes theoretically very low efficiency. This is because there is an non-constant pressure gas inlet process when the high pressure gas inlet valve is opened, which is an irreversible process. On the other hand, there is non-constant pressure gas outlet process when the low pressure gas outlet valve is opened, which is also an irreversible process. This necessarily causes a large irreversible loss. These two processes cause theoretically very low efficiency of the orifice type pulse tube refrigerator. That is, the efficiency is poor in such a pulse tube refrigerator as produces cold by forming phase displacement with orifice because irreversible loss occurs when gas passes through the orifice. However, a theoretical efficiency in a perfect cycle reaches 100%. When the pulse tube refrigerator is used in case of a small refrigeration power, this disadvantage is not obvious. However, in case for necessity of large refrigeration power, this disadvantage becomes very conspicuous.